The present invention deals with qualifying hard disk drives. More specifically, the present invention deals with detecting amplitude modulation on a written signal on a disc drive as a result of head movement in the z-axis during the write operation.
A typical disc drive includes one or more discs mounted for rotation on a hub or spindle. A typical disc drive also includes one or more transducers supported relative to surfaces of the discs in the disc drive to read information from, and write information to, the discs. The transducers along with any air bearings associated therewith are collectively referred to as a data head. A drive controller is conventionally used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to retrieve information from the disc and to store information on the disc.
An actuator operates within a servo system and typically includes an actuator arm that supports a flexure or flexure assembly which, in turn, supports the data head. The actuator moves the data head radially over the disc surface for track seek operations and holds the transducer directly over a track on the disc surface for track following operations.
Information is typically stored on the discs by providing a write signal to the data head to encode information on the surface of the disc representing the data to be stored. In retrieving data from the disc, the drive controller controls the actuator so that the data head flies above the disc, sensing the information on the disc, and generating a read signal based on that information. The read signal is then decoded by the drive controller to recover the data represented by the information stored on the disc, and consequently represented in the read signal provided by the data head.
An emerging market for disc drives involves home entertainment systems. In such systems, a user may wish to simultaneously record several channels of television programming, play a movie, download compact disc-quality music from a global network, and host a network game, all using a single audio visual video controller.
In order to accomplish all of these tasks, the disc drive must be able to retrieve its data without interrupting the incoming data stream. That is, it must continue to be able to record television transmission (for example) in real time while playing back compact disc quality music (for example) stored on the disc drive. Such operations require the drive to seek constantly between two different locations on the disc. One location is designated for recording the incoming information and the other is designated for reading back information which was previously stored. These types of operations demand the disc drive write and read operations to be performed at an ever increasing speed.
The present invention addresses one or more of these and other problems, and offers advantages over the prior art.
It has been found that one effect of very fast read/write operations is that the data heads may not have sufficiently stabilized after moving from a previous location on a track prior to beginning to write a new location on another track. If head movement happens to be in the z-axis (normal to the surface of the disc) the written signal will exhibit an amplitude modulation (due to head movement in the z-axis) potentially causing unreadable data.
The present invention is directed to detecting amplitude modulation on the written signal as a result of head movement along the z-axis during the write operation, before the head has had sufficient time to stabilize after seeking from a different track.
In one embodiment, the transducer is positioned at an origin location on an origin cylinder. The drive then repeatedly seeks from the origin location to a destination test location on a destination cylinder. For each seeking step, test data is written to the destination test location within approximately two milliseconds (2 ms) of an end of the seeking step. The data is then read and errors are detected in the data read from the destination test location. These errors can be used to detect amplitude modulation on the written signal.
In another embodiment, a minimum seek destination location on a destination cylinder is identified as a location which has a minimum seek time from a chosen location on an origin cylinder. Based on the minimum seek location, a destination test location is chosen which has a predetermined offset on the destination cylinder. Seek operations are then performed from the origin location to the destination test location. For each seeking step, data is written to the destination test location and is read back. Errors are detected at the destination test location by determining whether the data to be written to the destination test location was actually read. These errors are used to qualify the disc drive.